Rotating-element ellipsometer and method for measuring properties of the sample using the same

ABSTRACT

Provided is a real-time spectroscopic ellipsometer capable of obtaining information on properties of a sample, a nano pattern shape, and the like, in real time by measuring and analyzing, for a plurality of wavelengths, a change in a polarization state of incident light generated while being reflected or transmitted due to the sample when light having a specific polarization component is incident to the sample. The real-time spectroscopic ellipsometer according to the exemplary embodiment of the present invention have the improved structure and function to solve problems such as polarization dependency of a light source and a photometric detector, wavelength dependency of a compensator, a limitation of a change in integration time due to a fixing of a measuring frequency of exposure, in a rotating-element multichannel spectroscopic ellipsometers of the related art, thereby measuring more accurately, precisely, and rapidly measuring the characteristics of the sample than the related art.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Korean PatentApplication No. 10-2011-0081475, filed on Aug. 17, 2011, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The following disclosure relates to a rotating-element multichannelellipsometer, and more particularly, to a real-time ellipsometer used tomeasure properties of a sample by measuring and analyzing a change in apolarization state of light reflected or transmitted by the sample inreal time.

BACKGROUND

Importance of a technology capable of measuring and evaluatingproperties such as optical properties, a shape of nano patterns, and thelike, of nano samples in real time by a non-destructive manner or anon-contact manner during a manufacturing process, in industrial fieldsrelated to a semiconductor device, a flat panel display, nanobio,nanoimprint, thin film optics, and the like, which have been rapidlydeveloped has been gradually increased. Therefore, in an ellipsometryused as measuring equipment for process in the industrial fields, themeasuring precision and measuring accuracy have been gradually improvedand the continuous improvement of a measuring speed for real-timemeasurement has been required.

A multichannel spectroscopic ellipsometer as shown in FIG. 1 amongmultichannel spectroscopic ellipsometers of the related art has been themost widely used. The multichannel spectroscopic ellipsometer has beenwell known as nano measuring equipment that uses a basic principle ofmeasuring and analyzing a change in a polarization state of reflectedlight 300 or transmitted light by the sample 200 for a plurality ofwavelengths when incident light 100 is incident to the sample 200 tofind properties of the sample.

Describing core components of the multichannel spectroscopicellipsometers of the related art, a light source 110, an achromaticaberration collimator 120 that changes light emitted from the lightsource 110 into parallel light, and a polarization modulation unit 125that forms the parallel light into a specific polarization state aredisposed on a line of the incident light 100 and a polarization analysisunit 305 that is an optical system for analyzing the polarization stateof the reflected light, and an achromatic aberration optical focussystem 330 that intensively irradiates the parallel light transmittingthe polarizing analysis unit 305 on a local area is disposed on a lineof the reflected light 300, wherein the intensively irradiated lighttransmits an optical fiber 340 or is directly incident to a slit of amultichannel spectrometer 350. The multichannel spectrometer includes adispersion optical system 352 and a multichannel photometric detector354 and the light transmitting the slit is dispersed by the dispersionoptical system 352 to be irradiated on each pixel of the multichannelphotometric detector 354 for each wavelength and a quantity of lightincident to each pixel is measured as an electrical signal such asvoltage or current.

Among various types of multichannel spectroscopic ellipsometers of therelated art, a rotating-polarizer or analyzer spectroscopic ellipsometerand a rotating-compensator spectroscopic ellipsometer have been the mostwidely used, each of which uses a least-squares algorithm analysismethod that measures Fourier coefficients or ellipsometric functionsabout a waveform of the intensity of light measured by the photometricdetector when a linear polarizer or a compensator rotates at apredetermined speed by a multichannel photometric detector in real timeand uses the measured values and a theoretical model for a sample tofind properties of a sample.

A core component of the rotating-polarizer multichannel spectroscopicellipsometers of the related art is configured of a linear polarizer inwhich the polarization modulation unit 125 rotates at constant velocityof FIG. 1, which is generally referred to as the polarizer. Thepolarization analysis unit 305 is configured of a linear polarizer thatstops at any azimuth, which is generally referred to as an analyzer.Meanwhile, core components of the rotating-analyzer multichannelspectroscopic ellipsometer are the same as the components of therotating-polarizer multichannel spectroscopic ellipsometer except thatthe polarizer, that is, the polarization modulation unit 125 is in astop state and the analyzer instead rotates at constant velocity.Therefore, the rotating-polarizer (or analyzer) multichannelspectroscopic ellipsometers of the related art have the most idealadvantage in terms of spectroscopic measurement since the number ofconfigured optical elements is relatively smallest and only the opticalelements of achromatic aberration such as a prism linear polarizer areused. However, the rotating-polarizer multichannel spectroscopicellipsometers of the related art have a critical disadvantage calledresidual polarization of the light source and the rotating-analyzermultichannel spectroscopic ellipsometers need to solve the polarizationdependency problem of the photometric detector by calibration.

Meanwhile, the rotating-compensator multi-channel spectroscopicellipsometers of the related art may be classified into a singlerotating compensator and a double rotating compensator. First, the corestructure of the single rotating-compensator multichannel spectroscopicellipsometers is the same as the core structure of therotating-polarizer multichannel spectroscopic ellipsometers of therelated art except that the polarizer stops and the compensator rotatingat constant velocity is added between the polarizer and the sample orbetween the sample and the analyzer.

Meanwhile, the core structure of the double rotating-compensatormultichannel spectroscopic ellipsometers of the related art has the samestructure of the single rotating-compensator multichannel spectroscopicellipsometers of the related art except that one compensator is furtheradded so that the compensators are each disposed at both sides of thesample, wherein these compensators each rotate at a uniform velocityratio of an integer. Therefore, in the core structure of therotating-compensator multichannel spectroscopic ellipsometers of therelated art, the polarizer and the analyzer are in a stop state at thetime of measurement. Therefore, the rotating-compensator multichannelspectroscopic ellipsometers of the related art does not have a problemof the polarization dependency problem of the light source and thephotometric detector. However, for a broadband wavelength λ region, itis very difficult to manufacture the achromatic aberration compensatorhaving a phase difference of λ/4. As a result, there are problems interms of dispersion characteristics and equipment calibration of thecompensator, complexity of a method for analyzing data, and the like.

Meanwhile, in order to obtain the Fourier coefficients or theellipsometric functions for the waveform of the intensity of light, therotating-element multichannel ellipsometers of the related art uses afixed exposure measuring frequency per unit rotation and a fixedintegration time of the multichannel photometric detector that is equalto an exposure measuring period. In order to measure the Fouriercoefficients or the ellipsometric functions, the rotating-elementmultichannel ellipsometers of the related art adopts a method formeasuring the exposure of a predetermined frequency M per unitmeasurement by each pixel of the multichannel photometric detector at aplurality of azimuths at equidistance for one turn period or a half ofthe turn period of the optical element while at least one opticalelement rotating at constant velocity. The rotating-polarizer oranalyzer multichannel spectroscopic ellipsometers of the related artmainly use the case in which the exposure measuring frequency M per unitmeasurement is fixed to 4, the single rotating-compensator mutlichannelspectroscopic ellipsometers of the related art mainly use the case inwhich M is fixed to 8, and the double rotating-compensator mutlichannelspectroscopic ellipsometers of the related art mainly use the case inwhich M is fixed to 36.

Meanwhile, in the case of the rotating-element ellipsometers of therelated art, since the difference in the intensity of light reflected ortransmitted by the sample according to the material and structure of thesample is generally large, the integration time needs to increase so asto reduce the measuring error when the intensity of light to be measuredis weak, but may be limited by the predetermined exposure measuringperiod.

To the contrary, when the measured intensity of light is excessivelylarge, the photometric detector reaches a saturation state andtherefore, the integration time needs to be reduced. In this case, asthe integration time is smaller than the exposure measuring period, thestandby time of the photometric detector is longer and longer, such thatthe measuring precision may be deteriorated.

When the intensity of light periodically changing over time t ismeasured in real time by using the integrating photometric detector, therotating-element ellipsometer uses a method for analyzing a Fouriercoefficient so as to analyze the waveform. Provided that there is noerror in the measuring apparatus, the light intensity I(t) measured bythe integrating photometric detector using electrical signal such asvoltage or current for a specific wavelength may be represented by thefollowing Equation.

$\begin{matrix}{{I(t)} = {I_{dc}\left\{ {1 + {\sum\limits_{n = 1}^{N}\; \left\lbrack {\alpha_{2\; n}{\cos \left( {4\; \pi \; {{nt}/T}} \right)}\beta_{2\; n}{\sin \left( {4\; \pi \; {{nt}/T}} \right)}} \right\rbrack}} \right\}}} & (1)\end{matrix}$

In the above equation, I_(dc) represents an average value of theintensity of light (or referred to as a 0-order Fourier coefficient),α_(2n) and β_(2n) represent normalized Fourier coefficients, and Trepresents a period. Here, 2N is not 0 but is a natural number thatrepresents a highest order among the normalized Fourier coefficients.

Among various types of the rotating-element multichannel ellipsometersof the related art, in the case of the rotating-polarizer orrotating-analyzer multichannel ellipsometers of the related art, all theFourier coefficients other than the normalized Fourier coefficients of asecondary term such as α2 and β2 in Equation (1) that is the intensityof light measured by the multichannel photometric detector have a valueof 0 and therefore, N becomes 1.

In the case of the single rotating-compensator multichannelellipsometers of the related art, only the Fourier coefficients ofsecond and fourth-order terms such as α₂, β₂, α₄, and β₄ are not 0 andtherefore, N becomes 2. Meanwhile, in the case of the doublerotating-compensator ellipsometers of the related art, the Fouriercoefficients of the effective highest order term in Equation (1) are α₃₂and β₃₂ when two compensators rotate at constant velocity at apredetermined velocity ratio of 5:3 and therefore, N becomes 16.

In the multichannel ellipsometers, a method of more accurately obtainingthe normalized Fourier coefficients α_(2n) and β_(2n) from the waveformof the intensity of light measured by the photometric detector as in theabove Equation 1 is very important. The rotating-element multichannelellipsometers of the related art that are the most widely spread havemainly used a CCD detector array, a photodiode detector array, and thelike, as the multichannel photometric detector. The multichannelphotometric detectors are referred to as the integrating photometricdetector since the measured light quantity value is proportional to theintensity of light as well as integration time. The integratingphotometric detector reduces or increases the integration time when thequantity of light is too large or insufficient at the time ofmeasurement to perform the measurement under the appropriate conditions.However, the integration time needs to be equal or larger to or than theminimum integration time of the corresponding photometric detector atthe time of measurement.

In order for the rotating-element multichannel ellipsometers of therelated art to obtain the Fourier coefficients, the intensity of lightperiodically changing over time as in the equation (1) is measured bybeing divided M times per unit measurement at a predetermined timeinterval by the multichannel integrating photometric detector. In thiscase, the integration time accurately coincides with the divided timeinterval. For example, the exposure S_(j) measured under the conditionsof, for example, T_(i)=T/M is represented by the following Equation (2).

$\begin{matrix}\begin{matrix}{{S_{j} = {\int_{{({j - 1})}{T/M}}^{{jT}/M}{{I(t)}\ {t}}}},\left( {{j = 1},2,3,\ldots \mspace{14mu},M} \right)} \\{= {\frac{I_{dc}T}{M} + {\sum\limits_{n = 1}^{N}\; {\frac{I_{dc}T}{2\; n\; \pi}{\sin \left( \frac{2\; n\; \pi}{M} \right)}\begin{Bmatrix}{{\alpha_{2\; n}{\cos \left\lbrack \frac{2\; n\; {\pi \left( {{2\; j} - 1} \right)}}{M} \right\rbrack}} +} \\{\beta_{2\; n}{\sin \left\lbrack \frac{2n\; {\pi \left( {{2\; j} - 1} \right)}}{M} \right\rbrack}}\end{Bmatrix}}}}}\end{matrix} & (2)\end{matrix}$

When solving the normalized Fourier coefficient by a simultaneousequation like the above Equation (2), the Equation of the normalizedFourier coefficients α_(2n) and β_(2n) represented by the exposure S_(j)is obtained, which is referred to as Hadamard transform and has beenused as a representative method of obtaining Fourier coefficients in therotating-element multichannel ellipsometers of the related art.Therefore, only the multichannel integrating photometric detectorsspecially designed and manufactured to satisfy the conditions is used.However, the actual integrating photometric detectors read out thequantity of light accumulated in each pixel for the integration time anddo not react with the incident light for the time initializing thestate, that is, the readout time T_(r). Therefore, the exposure of theabove Equation (2) is corrected to the following Equation (3) inconsideration of this situation.

S _(j)=∫_((j-1)T/M+T) _(r) ^(jT/M) I(t)dt,(j=1,2,3, . . . ,M)  (3)

In this case, under the assumption that the readout time T_(r) is veryshorter than the measuring time interval T/M of exposure, an equationobtained by performing first-order approximation on T_(r) is used.

In the case of the rotating-polarizer or analyzer multichannelellipsometers of the related art using the Hadmard transform, in theabove Equation (1), T represents a mechanical turn period of thepolarizer or the analyzer, N is 1 as described above, and the minimumvalue of the measuring frequency M of exposure measured for period T/2is 3. However, β₄ is additionally measured in order to see whether thesystem is in a normal state and thus, the measuring frequency ofexposure is increased to 4. In this case, since the exposure valuesmeasured in each period have symmetry with respect to a period of T/2,four unknown coefficients I_(dc), α₂, β₂, and β₄ can be measured from asimultaneous equation configured of only S₁, S₂, S₃, and S₄ measured ata first half period.

Meanwhile, in the case of the single rotating-compensator multichannelellipsometers of the related art using the Hadamard transform, Trepresents the mechanical turn period of the compensator, N is 2, andthe minimum value of the frequency M of exposure measured for period T/2is 5. However, β₈ is additionally measured so as to see whether thesystem is in a normal state and thus, the measuring frequency ofexposure is increased to 8. In order to obtain six unknown coefficientsI_(dc), α₂, β₂, α₄, β₄, and β₈ from the measured value of S_(j) (j=1, 2,3, . . . , 8) in consideration of the symmetry of the value of exposuremeasured like the previous case, the solution of simultaneous equationis used. In addition, in the case of the double rotating-compensatormultichannel ellipsometers of the related art using the Hadamardtransform, thirty six unknown coefficients are each obtained in a verycomplex form by solving thirty six simultaneous equations.

In the rotating-element multichannel ellipsometers of the related art,when the turn period of the optical element is T, the measured period islimited to T/2 or T and equations of different complex forms obtained bysolving the simultaneous equation of Equation (2) for the measuringfrequency M of exposure per unit measurement one by one are used. Inaddition, a method for correcting the readout time error by using thefirst-order approximation equation for the readout time for Equation (3)for the measured values S_(j) of exposure to obtain the average valueI_(dc) of the intensity of light and the normalized Fourier coefficientsα_(2n) and β_(2n) is used. Therefore, the integration time of thephotometric detector used in the rotating-element multichannelellipsometers of the related art is fixed to T/M or has only a valuesmaller than T/M and as a result, it is impossible to increase theintegration time by reducing the measuring frequency of exposure orchanging the measuring period.

When using the Hadamard transform of the related art, a sum of thereadout time and the integration time needs to be set to accuratelycoincide with the measuring time interval. Therefore, when the intensityof light is too strong, the quantity of light easily reaches thesaturation state even for the short integration time and thus, a part oflight beam needs to be blocked by additionally using the opticalelements such as an iris diaphragm, a neutral density filter (NDfilter), and the like, inevitably so as to reduce the output from thelight source. To the contrary, when the intensity of light is weak,there is a need to increase the integration time, but an apparatus forthe measuring period and the measuring frequency of exposure speciallyset according to a kind of the multichannel ellipsometers of the relatedart is configured and used and thus, the maximum value of theintegration time may be limited to T/M.

A need exists for a development of new multichannel ellipsometerscapable of solving the above problems.

RELATED ART DOCUMENT Patent Document

-   (Patent Document 1) KR 742982 B Jul. 20, 2007-   (Patent Document 2) KR 2009-49226 A May 18, 2009-   (Patent Document 3) KR 2011-35811 Apr. 6, 2011

SUMMARY

An exemplary embodiment of the present invention is directed toproviding a rotating-element ellipsometer capable of more easily andprecisely measuring Fourier coefficients for a waveform of the intensityof light by solving problems of complexity of equipment or degradationof measuring precision due to addition of an optical system caused bylimiting integration time of a photometric detector of arotating-element ellipsometer of the related art.

Another exemplary embodiment of the present invention is directed toproviding a rotating-element ellipsometer capable of accuratelymeasuring properties of a sample by more precisely acquiring Fouriercoefficients for a waveform of the intensity of light by simplecalculation.

Another exemplary embodiment of the present invention is directed toproviding a rotating-element ellipsometer with improved measuringprecision by rapidly and easily changing integration time and ameasuring frequency of exposure with computer software.

Another exemplary embodiment of the present invention is directed toproviding a multichannel spectroscopic ellipsometer capable ofaccurately measuring properties of a sample in real time by solving aresidual polarization problem of a light source or a polarizationdependency problem of a photometric detector, a wavelength dependencyproblem of a compensator, problems such as a limitation of a change inintegration time due to a fixing of a measuring period and a measuringfrequency of exposure, and the like, in a rotating-element multichannelspectroscopic ellipsometers of the related art.

Another exemplary embodiment of the present invention is directed toproviding a multichannel spectroscopic ellipsometer configured of threepolarizers with the improved structure and function so as to moreaccurately and rapidly measure properties of a sample than the relatedart.

Another exemplary embodiment of the present invention is directed toproviding a rotating-polarizer multichannel spectroscopic ellipsometercapable of solving a residual polarization problem of a light source.

Another exemplary embodiment of the present invention is directed toproviding a rotating-analyzer multichannel spectroscopic ellipsometerwith improved measuring accuracy by solving a polarization dependencyproblem of a photometric detector.

An exemplary embodiment of the present invention provides anellipsometer including a light source, a polarization modulating unit, asample stage, a polarization analysis unit, and a photometric detector,the ellipsometer including a digital signal modulating apparatusconnected to an optical element unit rotating at constant velocity ofthe polarization modulating unit or the polarization analysis unit tocontrol a measuring frequency of exposure of the photometric detector.The digital signal modulating apparatus may be connected to thephotometric detector and may receive a pulse signal from the opticalelement unit and transmit a signal controlling the measuring frequencyof exposure of the photometric detector according to the measuringconditions and the photometric detector may measure the exposurecorresponding to the measuring frequency accordingly. The measuringconditions may be the intensity of light and the digital signalmodulating apparatus may control integration time and the measuringfrequency of exposure of the photometric detector according to theintensity of light.

The integration time and the measuring frequency of exposure may becontrolled by computer program.

The intensity of light may be changed at a predetermined period overtime and the ellipsometer according to the exemplary embodiment of thepresent invention includes an operator, wherein the operator acquires aplurality of values of exposure for a waveform of the intensity of lightat a predetermined interval for any multiple of the period from thephotometric detector and performs discrete Fourier transform on theplurality of values of exposure to determine a plurality of Fouriercoefficients and average value component for the waveform of theintensity of light.

An Equation about the value of exposure S_(j) may beS_(j)=∫_((j-1)pT/M+T) _(d) ^((j-1)pT/M+T) ^(d) ^(+T) ^(i) I(t)dt, (j=1,2, 3, . . . , M) and non-normalized Fourier coefficients A_(2n) andB_(2n) of waveform of intensity of light and average value I_(dc) ofintensity of light may each

$A_{2\; n} = {\frac{\xi_{2\; n}}{T_{i}{\sin \left( \xi_{2\; n} \right)}}\left\{ {{a_{2\; n}{\cos \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}} - {b_{2\; n}{\sin \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}}} \right\}}$be$B_{2\; n} = {\frac{\xi_{2\; n}}{T_{i}{\sin \left( \xi_{2\; n} \right)}}\left\{ {{a_{2\; n}{\sin \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}} + {b_{2\; n}{\cos \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}}} \right\}}$I_(dc) = d₀/T_(i)

where,

{T: Dynamic turn period of optical element rotating at constant velocity

P: The number of measuring periods (positive multiple of ½)

M: Measuring frequency of exposure at predetermined time interval formeasuring period pT

T_(d): Delay time

T_(i): Integration time

${I(t)} = {I_{dc} + {\sum\limits_{n = 1}^{N}\; \left\lbrack {{A_{2\; n}{\cos \left( {4\; \pi \; {{nt}/T}} \right)}} + {B_{2\; n}{\sin \left( {4\; \pi \; {{nt}/T}} \right)}}} \right\rbrack}}$

I(t): Intensity of light

I_(dc): Average value of intensity of light or 0-order

Fourier Coefficient

A_(2n), B_(2n): Fourier coefficients

2N: Natural number representing highest order among Fourier coefficientsexcept for 0

$\left. {{\xi_{n} = \frac{n\; \pi \; T_{i}}{T}}{a_{2\; n} = {\frac{2}{M}{\sum\limits_{j = 1}^{M}\; {S_{j}{\cos \left( \frac{4\; n\; {\pi \left( {j - 1} \right)}p}{M} \right)}}}}}{b_{2\; n} = {\frac{2}{M}{\sum\limits_{j = 1}^{M}\; {S_{j}{\sin \left( \frac{4\; n\; {\pi \left( {j - 1} \right)}p}{M} \right)}}}}}{d_{0} = {\frac{1}{M}{\sum\limits_{j = 1}^{M}\; S_{j}}}}} \right\}$

The properties for the sample such as interfacial characteristic, a thinfilm thickness, a complex refractive index, a nano shape, anisotropiccharacteristic, surface roughness, a composition ratio, crystallinity,and the like, may be analyzed from the Fourier coefficients I_(dc)/I₀₀,A_(2n)/I₀₀, B_(2n)/I₀₀; n=1, 2, 3, . . . ) or (I_(dc)/I₀₀,A_(2n)/I_(dc), B_(2n)/I_(dc); n=1, 2, 3, . . . ), in which the commoncomponent I₀₀ is defined as I₀₀=R_(u)T_(s), R_(u) the non-polarizationreflectance of the sample, and T_(s) a term related to the transmittancein the straight-through optical configuration of the ellipsometer.

According to the exemplary embodiment of the present invention,ellipsometric functions may be obtained by limitedly selecting a part ofthe Fourier coefficients I_(dc), A_(2n), B_(2n); n=1, 2, 3, . . . ,).

The ellipsometer may be any one of a rotating-polarizer ellipsometer, arotating-analyzer ellipsometer, a single rotating-compensatorellipsometer, a double rotating-compensator ellipsometer, and othervarious rotating-element ellipsometers.

According to the exemplary embodiment of the present invention, a methodfor determining Fourier coefficients uses the ellipsometer. In thiscase, the intensity of light may be changed at a predetermined periodover time and a plurality of values of exposure for a waveform of theintensity of light at a predetermined interval for any multiple of theperiod may be acquired from the photometric detector and a plurality ofFourier coefficients and average value component for the waveform of theintensity of light may be determined by performing discrete Fouriertransform on the plurality of values of exposure. In this case, theEquation about the value of exposure S_(j) and the Equation of thenon-normalized Fourier coefficients A_(2n) and B_(2n) of the waveform ofthe intensity of light and the average value I_(dc) of the intensity oflight may be used.

Another exemplary embodiment of the present invention provides anellipsometer including: a light source emitting white light to a sampledisposed on a sample stage; an achromatic aberration collimator disposedbetween the light source and the sample stage on a progress path oflight and forming the white light emitted from the light source intoparallel light; a first polarizer disposed between the achromaticaberration collimator and the sample stage on the progress path of lightand receiving the parallel light and polarizing the parallel light; asecond polarizer disposed between the first polarizer and the samplestage on the progress path of light and receiving light transmitting thefirst polarizer and rotating at constant velocity for polarizing theincident light; a sample stage supporting the sample; a third polarizerreceiving light with the changed polarization state while beingreflected or transmitted by the sample after being polarized bytransmitting the second polarizer polarizing the incident light; anachromatic aberration optical focus system receiving the lighttransmitting the third polarizer and intensively irradiating theincident light to a local region of a multichannel spectrometer; and amultichannel spectrometer receiving the light transferred by theachromatic aberration optical focus system, separating the incidentlight for each wavelength using the dispersion optical system,irradiating the light separated for each wavelength to the multichannelphotometric detector, and measuring the exposure of light irradiated tothe multichannel photometric detector for each pixel of the multichannelphotometric detector, whereby properties of the sample are measured.

Another exemplary embodiment of the present invention provides anellipsometer including: a light source emitting white light to a samplestage; an achromatic aberration collimator disposed between the lightsource and the sample stage on a progress path of light and forming thewhite light emitted from the light source into parallel light; a firstpolarizer disposed between the achromatic aberration collimator and thesample stage on the progress path of light and receiving the parallellight and polarizing the parallel light; a sample stage supporting thesample; a second polarizer receiving the light polarized by transmittingthe first polarizer and having the changed polarization state whilebeing reflected or transmitted by the sample and rotating at constantvelocity for polarizing the incident light; a third polarizer receivinglight transmitting the second polarizer and polarizing the incidentlight; an achromatic aberration optical focus system receiving the lighttransmitting the third polarizer and intensively irradiating theincident light to a local region of a multichannel spectrometer; and amultichannel spectrometer receiving the light transferred by theachromatic aberration optical focus system, separating the incidentlight for each wavelength using the dispersion optical system,irradiating the light separated for each wavelength to the multichannelphotometric detector, and measuring the exposure of light irradiated tothe multichannel photometric detector for each pixel of the multichannelphotometric detector, whereby properties of the sample are measured.

The ellipsometer may include the digital signal modulating apparatus forcontrolling the number of measuring periods and the measuring frequencyof exposure by the computer program and the digital signal modulatingapparatus may control the integration time of the photometric detectoraccording to the intensity of light irradiated to the multichannelphotometric detector.

The ellipsometer may perform the discrete Fourier transform on theexposure measured for the integration time arbitrarily set by themultichannel photometric detector at a predetermined time interval fortime (pT: p=½, 1, 3/2, 2, . . . ) of a multiple of ½ of the opticalelement turn period T to calculate the plurality of Fourier coefficientsI_(dc), A₂, B₂, A₄, and B₄. The ellipsometer may include an operatorperforming the calculation.

ψ, Δ, and R_(u) or N, C, and R_(u) may be calculated from at least threeof the plurality of Fourier coefficients.

The properties for the sample such as interfacial characteristic, a thinfilm thickness, a complex refractive index, a nano shape, anisotropiccharacteristic, surface roughness, a composition ratio, crystallinity,and the like, may be analyzed from the measured Fourier coefficientsI_(dc)/I₀₀, A₂/I₀₀, B₂/I₀₀, A₄/I₀₀, and B₄/I₀₀ or I_(dc)/I₀₀, A₂/I_(dc),B₂/I_(dc), A₄/I_(dc), and B₄/I_(dc) or the measured ellipsometricfunctions ψ, Δ, and R_(u) or N, C, and R_(u).

The measuring data of the measured Fourier coefficients I_(dc), A₂, B₂,A₄, and B₄ or the measured ellipsometric functions ψ, Δ, and R_(u) or N,C, and R_(u) may be obtained, the optical theoretical Equation for thesample may be established, the data of the Fourier coefficients or theellipsometric functions calculated using the plurality of unknownparameters for the region set for the established theoretical Equationmay be obtained, the continuous function for the unknown parameters maybe obtained from the data obtained from the calculation, and theproperties of the sample may be obtained by optimizing the continuousfunction by applying the least-squares algorithm to the measuring data.

The multichannel photometric detector is configured of a CCD, a CMOS, ora photodiode, wherein the plurality of pixels may be arranged in alinear or two-dimensional plane structure.

The ellipsometer may include a remote light source blocking apparatusdisposed after the light source on the progress path of light andblocking the light irradiated to the sample from the light source by aremote control.

The ellipsometer according to the exemplary embodiment of the presentinvention may include: a first hollow shaft stepping motor attached tothe first polarizer to control an azimuth of the first polarizer; asecond hollow shaft stepping motor attached to the third polarizer tocontrol an azimuth of the third polarizer; a hollow shaft constantvelocity rotating motor attached to the second polarizer to rotate thesecond polarizer at constant velocity; and an optical encoder attachedto the hollow shaft constant velocity rotating motor to rotate togetherwith the hollow shaft constant velocity rotating motor and generatingone reference pulse and a plurality of clock pulses for each rotation.

The clock pulses generated from the encoder may be transferred to thedigital signal modulating apparatus and the digital signal modulatingapparatus may generate the specific number of spectrometer operatingtriggers at equidistance by the pulses. The generated spectrometeroperating triggers may be transferred to the multichannel spectrometerto measure the exposure for the integration time set at each pixelwhenever the multichannel photometric detector receives the spectrometeroperating trigger.

The digital signal modulating apparatus may change the measuring periodor the measuring frequency of exposure according to the intensity oflight irradiated to the multichannel photometric detector to control theintegration time of the photometric detector.

The ellipsometric functions may be obtained by limitedly selecting theFourier coefficients with relatively excellent signal to noise ratioamong the Fourier coefficients I_(dc), A₂, B₂, A₄, and B₄.

The ellipsometer according to the exemplary embodiment of the presentinvention may include the optical fiber disposed between the achromaticaberration optical focus system and the multichannel spectrometer. Theoptical fiber may be a single optical fiber. A light receiving unit sidemay be a bundle of a single optical fiber and a side connected to themultichannel spectrometer may be a bundle of a branched optical fiberformed of a bundle of at least two optical fibers.

Another exemplary embodiment of the present invention provides a methodfor measuring properties of a sample using a multichannel spectroscopicellipsometer according to an exemplary embodiment of the presentinvention including: inputting the number p of measuring period, ameasuring frequency M of exposure, and integration time T_(i) bycomputer program; generating a reference pulse and a clock pulse by anencoder of a regular velocity rotating motor; changing, by a digitalsignal modulating apparatus, clock pulse modulating program; issuing, bythe computer program, a measuring command to a multichannelspectrometer; waiting the multichannel spectrometer to preparemeasurement; measuring the exposure of light reflected or transmittedfrom the sample for integration time at each pixel of the multichannelphotometric detector by receiving a spectrometer operating triggergenerated by the digital signal modulating apparatus; and calculatingellipsometric functions from the measured values of exposure, wherebyproperties of the sample are measured.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a multichannel spectroscopicellipsometer according to the related art.

FIG. 2 is a schematic diagram of a multichannel spectroscopicellipsometer according to a first exemplary embodiment of the presentinvention.

FIG. 3 is a schematic diagram of a multichannel spectroscopicellipsometer according to a second exemplary embodiment of the presentinvention.

FIG. 4 is a conceptual diagram for describing an operation principle ofthe multichannel spectroscopic ellipsometer according to a firstexemplary embodiment of the present invention.

FIG. 5 is a flow chart for describing a method for changing a measuringfrequency of exposure using computer software according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF MAIN ELEMENTS

-   100: Incident light-   110: Light source-   120: Achromatic aberration collimator-   125: Polarization modulation unit-   130: First polarizer-   140: First hollow shaft stepping motor-   150: Second polarizer-   160: Hollow shaft constant velocity rotating motor-   200: Sample-   210: Sample stage-   300: Reflected light-   305: Polarization analysis unit-   310: Second hollow shaft stepping motor-   320: Third polarizer-   330: Achromatic aberration optical focus system-   340: Optical fiber-   350: Multichannel spectrometer-   352: Dispersion optical system-   354: Multichannel photometric detector-   410: Remote light source blocking apparatus-   420: Data transmission line-   430: Digital signal modulating apparatus-   440: Data transmission line-   450: Achromatic aberration optical focus system-   460: Achromatic aberration collimator-   500: Incident surface-   510: Incident reference axis-   520: First polarizer transmitting axis direction-   530: Second polarizer transmitting axis direction-   540: Third polarizer transmitting axis direction

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments will be described in detail withreference to the accompanying drawings so that the present invention canbe easily practiced by those skilled in the art to which the presentinvention pertains. However, in describing embodiments of the presentinvention, detailed descriptions of well-known functions orconstructions will be omitted so as not to obscure the description ofthe present invention with unnecessary detail.

In addition, like or similar reference numerals denote parts performingsimilar functions and actions throughout the drawings. In addition,unless explicitly described otherwise, “comprising” any components willbe understood to imply the inclusion of other components but not theexclusion of any other components.

A configuration and a function of a rotating-element multichannelspectroscopic ellipsometer according to an exemplary embodiment of thepresent invention will be described below. First, FIGS. 2 and 3 arediagrams schematically showing a configuration of a multichannelspectroscopic ellipsometer according to an exemplary embodiment of thepresent invention for achieving the above objects.

As shown in FIG. 2, the multichannel spectroscopic ellipsometeraccording to the exemplary embodiment of the present invention mayinclude a light source 110, an achromatic aberration collimator 120, afirst polarizer 130, a first hollow shaft stepping motor 140, a secondpolarizer 150, a hollow shaft constant velocity rotating motor 160, asample 200, and a sample stage 210 that are disposed on a path ofincident light 100 and a second hollow shaft stepping motor 310, a thirdpolarizer 320, an achromatic aberration optical focus system 330, anoptical fiber 340, and a multichannel spectrometer 350 that are disposedon a path of reflected light 300, and the like.

In FIG. 2, the light source 110 may be a xenon lamp, a tungsten-halogenlamp, a deuterium lamp, and the like, or may be a lamp that transferslight emitted from the lamp through an optical fiber, and the like,wherein the white incident light 100 emitted from the light source 110is changed into a parallel light by the achromatic aberration collimator120.

The parallel light transmitting the achromatic aberration collimator 120is linearly polarized by the first polarizer 130 and a transmitting-axisdirection of the first polarizer stops at a position of an azimuth Pwith respect to the incident surface as shown in FIG. 4. The linearpolarization transmitting through the first polarizer transmits thesecond polarizer 150 attached to the hollow shaft motor 160 rotating atconstant velocity and then, is incident to a top surface of the sample200. In this case, in the transmitting-axis direction of the secondpolarizer attached to the hollow shaft motor rotating at constantvelocity, an azimuth P_(r) with respect to an incident surface 500 isdescribed with P_(r) as shown in FIG. 4 and rotates at constant velocityover time.

When the polarization state is changed due to the reflection by thesample 200, the reflected light 300 having only polarization componentsin a direction in which the azimuth with respect to the incident surfaceis A as shown in FIG. 4 is transmitted by the third polarizer 320. Thelinearly polarized parallel light transmitting the third polarizer iscondensed to a local area by the achromatic aberration optical focussystem 330, the condensed light transmits the optical fiber 340 ordirectly irradiated and transferred to a slit of the multichannelspectrometer 350 and the light transferred to the multichannelspectrometer 350 is separated for each wavelength by a dispersionoptical system 352 and irradiated to the multichannel photometricdetector 354, the light irradiated to the multichannel photometricdetector 354 is obtained as the value, that is, the exposure obtained bymeasuring the quantity of light for each wavelength for thepredetermined integration time T_(i) by each pixel of the multichannelphotometric detector 354, and Fourier coefficients, ellipsometric anglesψ and Δ, and unpolarized reflectivity R_(u) are operated from themeasured exposure. The multichannel spectroscopic ellipsometerpreferably includes an operation processor (not shown) for operation.

A theoretical equation for the ellipsometric function suitable for thesample is set and usable property information for the sample such as athin film thickness, a refractive index, a shape dimension of a nanopattern, and the like, can be obtained by analysis of a least-squaresalgorithm so that the theoretical equation is optimized for the measuredvalue.

FIG. 3 shows a multichannel spectroscopic ellipsometer according toanother exemplary embodiment of the present invention. In FIG. 2, theposition of the second polarizer 150 and the hollow shaft constantvelocity rotating motor 160 is changed and disposed on the path of thereflected light after the sample 200 on the optical path.

In FIGS. 2 and 3, the polarizers mainly use a prism type of a linearpolarizer that is made of MgF₂, SiO₂, CaCO₃, YVO₄, or a-BBO crystal, andthe like.

In the exemplary embodiment of FIGS. 2 and 3, the first polarizer 130and the third polarizer 320 may be each attached to the hollow shaftstepping motors 140 and 310 to control each azimuth through a computerand is in a stop state at the time of measurement.

In the rotating-polarizer multichannel spectroscopic ellipsometer of therelated art, the light source needs to have characteristics in which theintensity of light is constant with respect to all the polarizationdirections. In the rotating-polarizer multichannel spectroscopicellipsometer of the related art, as the light source, a xenon lamp, atungsten-halogen lamp, a deuterium lamp, or a light source apparatusdevised to simultaneously emit light by the deuterium lamp and thetungsten-halogen lamp are mainly used. The light source apparatuses havethe residual polarization characteristics in which the intensity oflight partially polarized in a direction is relatively larger than otherdirections and therefore, the spectroscopic ellipsometers need tocorrect error due to the residual polarization.

As described above, since it is difficult to implement a light sourceapparatus having no residual polarization in the rotating-polarizermultichannel spectroscopic ellipsometer of the related art, therotating-element multichannel spectroscopic ellipsometer of the presentinvention instead uses the linearly polarized light source byadditionally introducing the first polarizer 130 in a stop state betweenthe light source 110 and the second polarizer 150 rotating at constantvelocity to solve the residual polarization problem of the light source.

In the case of the rotating-analyzer multichannel spectroscopicellipsometers of the related art, in order to accurately measure thestate in which the polarization state of the light incident to thesample is changed due to the reflection or transmission due to thesample, the multichannel spectrometer capable of measuring the intensityof light incident to the multichannel spectrometer independent of thepolarization direction is used. However, in the multichannelspectrometers used in the rotating-analyzer multichannel spectroscopicellipsometers of the related art, a reflective dispersion opticalsystems such as a reflection mirror for collimation and a diffractinggrating is used and when the linear polarization having the constantintensity of light is transferred to the multichannel spectrometer, theintensity of light may be differently measured according to the changeof the polarization direction of the transferred light. Therefore, inthe rotating-element multichannel spectroscopic ellipsometers of thepresent invention, as shown in FIG. 3, the third polarizer 320 in thestop state is additionally mounted between the second polarizer 150rotating at constant velocity and the optical focus system 330 totransfer only the linear polarization in a specific polarizationdirection to the multichannel spectrometer 350, thereby solving thepolarization dependency problem of the multichannel spectrometer due tothe change in the polarization direction.

In the multichannel spectroscopic ellipsometer of the present invention,the optical fiber 340 is formed of a single optical fiber or a lightreceiving unit side is formed of a bundle of a single optical fiber anda side connected to the multichannel spectrometer may use a bundle ofbranched optical fiber formed of a bundle of at least two opticalfibers. The dispersion optical system 352 may be configured of a slitand a diffracting grating or only the diffracting grating. Themultichannel photometric detector 354 is configured of a CCD, a CMOS, ora photodiode device, wherein a plurality of pixels are arranged in alinear or two-dimensional plane structure. The multichannel spectrometer350 has a function of maintaining a standby state before the externaltrigger is transferred and then, starting to measuring the quantity oflight for the integration time set for each pixel of the multichannelphotometric detector 354 when the external trigger is transferred andselectively includes a buffer memory for arbitrarily storing themeasured data.

If it is assumed that there is no error in the rotating-elementmultichannel ellipsometer, the Equation (1) about the intensity of lightmeasured by the photometric detector using the electrical signal such asvoltage or current for the specific wavelength may be represented by thefollowing Equation (4).

$\begin{matrix}{{I(t)} = {I_{dc} + {\sum\limits_{n = 1}^{N}\; \left\lbrack {{A_{2\; n}{\cos \left( {4\; \pi \; {{nt}/T}} \right)}} + {B_{2\; n}{\sin \left( {4\; \pi \; {{nt}/T}} \right)}}} \right\rbrack}}} & (4)\end{matrix}$

In the above Equation (4), I_(dc) may represent the average value of theintensity of light (referred to as a 0-order Fourier coefficient),A_(2n) and B_(2n) may represent the non-normalized Fourier coefficients,and T may represent the dynamic period of the optical element rotatingat constant velocity. The optical element rotating at constant velocityin the rotating-element ellipsometer is selected as the linear polarizeror the compensator and therefore, waveforms of 2n-order component havecharacteristics having a period of T/(2n) in the waveform of theintensity of light due to the optical symmetry thereof.

In the present invention, in order to analyze the waveform of theintensity of light periodically changing over time as in the above (4),when the exposure is measured by being divided M times at apredetermined time interval for the time when the p-th rotation of theoptical element rotating at constant velocity, that is, for themeasuring period pT by using the integration photometric detector 354,the exposure S_(j) measured for each pixel of the multichannelphotometric detector 354 for the specific delay time T_(d) and anyintegration time T_(i) of the multichannel photometric detector 354 maybe represented by the generalized Equation.

S _(j)=∫_((j-1)pT/M+T) _(d) ^((j-1)pT/M+T) ^(d) ^(+T) ^(i)I(t)dt,(j=1,2,3, . . . ,M)  (5)

In the above Equation (5), the delay time T_(d) may be changed accordingto the kind of the multichannel photometric detector 354 and has thespecific value. When the measuring command such as the external triggeris transferred to the multichannel spectrometer 350, the photometricdetector does not react with the received light for the measuringprepare time such as initializing the state of each pixel in themultichannel photometric detector 354 and therefore, the delay time isintroduced into the exposure Equation of Equation (5) in considerationof this aspect. When considering the symmetry of the rotating opticalelements such as the linear polarizer or the compensator in therotating-element ellipsometer according to the exemplary embodiment ofthe present invention, the value of the number p of measuring periodsmay be freely selected as one of multiples of ½ and therefore, themaximum value of the settable integration time can be changed to pT/M.However, in the related art, a value of p is fixed to ½ or 1 andtherefore, the maximum values of the set integration time each needs tobe set as T/(2M) or T/M.

When Equation (4) is substituted into Equation (5),

$\begin{matrix}{S_{j} = {{I_{dc}T_{i}} + {\sum\limits_{n = 1}^{N}\; {\frac{T}{2\; n\; \pi}{\sin \left( \frac{2\; n\; \pi \; T_{i}}{T} \right)}\begin{Bmatrix}{{{\cos \left( \frac{4\; n\; {\pi \left( {j - 1} \right)}p}{M} \right)}\begin{bmatrix}{{A_{2\; n}{\cos \left( \frac{2\; n\; {\pi \left( {T_{i} + {2\; T_{d}}} \right)}}{T} \right)}} +} \\{B_{2\; n}{\sin \left( \frac{2\; n\; {\pi \left( {T_{i} + {2\; T_{d}}} \right)}}{T} \right)}}\end{bmatrix}} -} \\{{\sin \left( \frac{4\; n\; {\pi \left( {j - 1} \right)}p}{M} \right)}\left\lbrack {\quad\begin{matrix}{{A_{2\; n}{\sin \left( \frac{2\; n\; {\pi \left( {T_{i} + {2\; T_{d}}} \right)}}{T} \right)}} -} \\{B_{2\; n}{\cos \left( \frac{2\; n\; {\pi \left( {T_{i} + {2\; T_{d}}} \right)}}{T} \right)}}\end{matrix}} \right\rbrack}\end{Bmatrix}}}}} & (6)\end{matrix}$

is obtained. The measuring Equation of exposure of Equation (6) uses thediscrete Fourier transform using orthogonality of a trigonometricfunction such as the following Equations (7), (8), and (9)

$\begin{matrix}{d_{0} = {\frac{1}{M}{\sum\limits_{j = 1}^{M}\; S_{j}}}} & (7) \\{a_{2\; n} = {\frac{2}{M}{\sum\limits_{j = 1}^{M}\; {S_{j}{\cos \left( \frac{4\; n\; {\pi \left( {j - 1} \right)}p}{M} \right)}}}}} & (8) \\{b_{2\; n} = {\frac{2}{M}{\sum\limits_{j = 1}^{M}\; {S_{j}{\sin \left( \frac{4\; n\; {\pi \left( {j - 1} \right)}p}{M} \right)}}}}} & (9) \\{I_{dc} = {d_{0}/T_{i}}} & (10) \\{A_{2\; n} = {\frac{\xi_{2\; n}}{T_{i}{\sin \left( \xi_{2\; n} \right)}}\begin{Bmatrix}{{a_{2\; n}{\cos \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}} -} \\{b_{2\; n}{\sin \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}}\end{Bmatrix}}} & (11) \\{B_{2\; n} = {\frac{\xi_{2\; n}}{T_{i}{\sin \left( \xi_{2\; n} \right)}}\begin{Bmatrix}{{a_{2\; n}{\sin \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}} +} \\{b_{2\; n}{\cos \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}}\end{Bmatrix}}} & (12)\end{matrix}$

In the above equation, the I_(dc) represents the average value of theintensity of light of Equation (4) and the non-normalized Fouriercoefficients A_(2n) and B_(2n) for any order 2n are obtained. Here,ξ_(n)=nπTi/T. d₀, a_(2n), and b_(2n) of Equations (7) to (9) areobtained from the exposure S_(j) measured for any integration time T_(i)at a predetermined time interval pT/M for the arbitrarily set measuringfrequency M for exposure and when these values are substituted intoEquations 10 to 12, experimental values for I_(dc), A_(2n), and B_(2n)can be obtained.

Generally, even though the light from the light source is blocked, themultichannel photometric detectors may have a background signal due tothermal noise and the unintended light by environmental lighting, andthe like and therefore, the error occurs when these aspects are notconsidered. Therefore, as shown in FIGS. 2 and 3, a remote light sourceblocking apparatus 410 is installed after the light source 110 on theoptical path to block the light emitted from the light source 110 beforemeasurement, thereby measuring the background signal. In this case, whenthe measured value of the background signal is subtracted from themeasured value of the exposure, the error due to the background signalis removed.

In the exemplary embodiment of the present invention, in order to moreeasily measure the Fourier coefficients for the waveform of theintensity of light, the digital signal modulating apparatus 430 as shownin FIGS. 2 and 3 is introduced so as to arbitrarily change the number ofmeasuring periods and the measuring frequency of exposure and thedetailed flow chart thereof is shown in FIG. 5. In this case, thedigital signal modulating apparatus 430 may be preferably configured ofa field-programmable gate array (FPGA) integrated circuit and a computercontrolling it but may appropriately use other processors.

As shown in FIGS. 2 and 3, the second polarizer 150 is attached to thehollow shaft motor 160 rotating at constant velocity at the time periodT, such that the second polarizer 150 and the hollow shaft motor 160rotate together. The hollow shaft motor 160 may change control inputvoltage to control a rotating speed. An optical encoder attached to thehollow shaft motor 160 generates one reference pulse for each rotationof the time period T and clock pulses that are set to be a naturalnumber of several hundreds or more. Here, the reference pulse is used tofind the reference point with respect to the incident surface of theazimuth of the second polarizer 150 of FIG. 4.

As shown in FIG. 5, in the rotating-element multichannel spectroscopicellipsometer according to the exemplary embodiment of the presentinvention, the value of the measuring frequency M of exposure per unitmeasurement is selected as one of divisors for a total number of clockpulses generated per unit measurement by the optical encoder and thepulse modulating program of the digital signal modulating apparatus 430can be changed by computer software. Therefore, the integration timeT_(i) of the multichannel photometric detector 354 may be set to beequal to or smaller than the value of pT/M and therefore, the maximumvalue of the integration time may be controlled by changing the M valueand the p value. When the clock pulses generated from the encoder aretransferred to the digital signal modulating apparatus 430 along asignal transmission line 420, the spectrometer operating triggers aregenerated by a total number M and an equidistance pT/M by the digitalsignal modulating apparatus 430. When the spectrometer operatingtriggers generated as described above are transferred to themultichannel spectrometer 350 by another signal transmission line 440,the exposure is measured for the integration time set at each pixelwhenever the multichannel photometric detector 354 receives thespectrometer operating triggers. d₀, a_(2n), and b_(2n) of Equations (7)to (9) are obtained from the exposure measured for the arbitrarily setmeasuring frequency M of exposure and when these values are substitutedinto Equations 10 to 12, the experimental values for I_(dc), A_(2n), andB_(2n) may be obtained. The ellipsometer includes an operator (notshown) performing the foregoing operation to acquire the pluralityvalues of exposure for the waveform of the intensity of light at apredetermined interval for any multiple of the period T from themultichannel photometric detector 354 and performs the discrete Fouriertransform on the plurality of values of exposure to determine theplurality of Fourier coefficients and the average value component of thewaveform of the intensity of light.

Finally, the ellipsometric functions are obtained from the measuredFourier coefficients.

In the rotating-element multichannel ellipsometers of the presentinvention as shown in FIGS. 2 and 3, the relationship Equation betweenthe ellipsometric angles ψ and Δ are obtained from the Fouriercoefficients related to the waveform of the intensity of light asdescribed above.

FIG. 4 is a diagram showing an azimuth of the polarizers of a case ofthe rotating-element multichannel spectroscopic ellipsometer accordingto an exemplary embodiment of the present invention as shown in FIG. 2.Here, the incident surface 500 is vertical to the surface of the sample200 and is defined as a plane in which the path of the incident light100 and the path of the reflected light 300 exists. When the incidentlight 100 is irradiated to a shaft 510 vertical to the sample 200 at anincident angle θ, the incident light 100 is reflected at the same angleθ by the sample 200 and thus, becomes the reflected light 300. Theazimuths of a transmitting axis 520 of the first polarizer, atransmitting axis 530 of the second polarizer, and a transmitting axis540 of the third polarizer for the incident surface 500 are eachrepresented by P, P_(r), and A. The hollow shaft stepping motor is usedin order to control the azimuths of the first polarizer and the thirdpolarizer and the hollow shaft constant velocity rotating motormanufactured by a DC motor, an AC motor, or a stepping motor is used inorder to rotate the second polarizer at constant velocity.

When the measuring system is applied to the sample having isotropicoptical characteristics as shown in FIG. 4, the incident light isdescribed by a Stokes vector and the polarizers and the sample are eachdescribed by a Mueller matrix to calculate the intensity of lighttransmitting the third polarizer for any one waveform. In this case, thefollow theoretical Equation is given.

$\begin{matrix}{{I\left( P_{r} \right)} = {I_{dc} + {A_{2}{\cos \left( {2\; P_{r}} \right)}} + {B_{2}{\sin \left( {2\; P_{r}} \right)}} + {B_{2}{\sin \left( {2\; P_{r}} \right)}} + {A_{4}{\cos \left( {4\; P_{r}} \right)}} + {B_{4}{\sin \left( {4\; P_{r}} \right)}}}} & (13) \\{I_{dc} = {\frac{I_{00}}{2}\left\{ {2 + {{\cos \left( {2\; A} \right)}{\cos \left( {2\; P} \right)}} - {N\left\lbrack {{2\; {\cos \left( {2\; A} \right)}} + {\cos \left( {2\; P} \right)}} \right\rbrack} + {C\; {\sin \left( {2\; A} \right)}{\sin \left( {2\; P} \right)}}} \right\}}} & (14) \\{\mspace{79mu} {A_{2} = {I_{00}\left\{ {{\cos \left( {2\; P} \right)} + {\cos \left( {2\; A} \right)} - {N\left\lbrack {1 + {{\cos \left( {2\; A} \right)}{\cos \left( {2\; P} \right)}}} \right\rbrack}} \right\}}}} & (15) \\{\mspace{79mu} {B_{2} = {I_{00}\left\{ {{\sin \left( {2\; P} \right)} - {N\; {\cos \left( {2\; A} \right)}{\sin \left( {2\; P} \right)}} + {C\; {\sin \left( {2\; A} \right)}}} \right\rbrack}}} & (16) \\{\mspace{79mu} {A_{4} = {\frac{I_{00}}{2}\left\lbrack {{{\cos \left( {2A} \right)}{\cos \left( {2\; P} \right)}} - {N\; {\cos \left( {2\; P} \right)}} - {C\; {\sin \left( {2\; A} \right)}{\sin \left( {2\; P} \right)}}} \right\rbrack}}} & (17) \\{\mspace{79mu} {B_{4} = {\frac{I_{00}}{2}\left\lbrack {{{\cos \left( {2A} \right)}{\sin \left( {2\; P} \right)}} - {N\; {\sin \left( {2\; P} \right)}} + {C\; {\sin \left( {2\; A} \right)}{\cos \left( {2\; P} \right)}}} \right\rbrack}}} & (18)\end{matrix}$

In the above Equations, N and C are functions defined by theellipsometric angles ψ and Δ like N=cos(2ψ) and C=sin(2ψ) cos(Δ) and thecommon component I₀₀ is defined by a product of T_(s) that is related totransmittance for the optical system of the ellipsometer bynon-polarization reflectivity R_(u) due to the sample. Even for thesamples having the anisotropic optical characteristics, an identicalequation for the Fourier coefficients may be induced using a methodsimilar to the foregoing method.

In the single channel spectroscopic ellipsometers configured of threepolarizer of the related art, an equation obtaining the ellipsometricfunctions ψ, Δ, and R_(u) using all the simultaneous equations for fourFourier coefficients are used is used and therefore, the measuringprecision may be relatively degraded. Therefore, when the simultaneousequation is solved by optionally selecting the Fourier coefficients withrelatively excellent measurement conditions to use the results obtainingthe solutions for N and C, the characteristic of the measuring precisionmay be better than the measured result of the related art.

The simultaneous equations (14) to (18) are described by three unknownparameters I₀₀, N, and C and therefore, at least three simultaneousequations are required to obtain the unknown parameters. When thesimultaneous equations (14) to (16) are selected,

$\begin{matrix}{I_{00} = \frac{\begin{matrix}{{2\left\lbrack {{2\; I_{dc}} - {A_{2}{\cos \left( {2\; P} \right)}} - {B_{2}{\sin \left( {2\; P} \right)}}} \right\rbrack} +} \\{{\cos \left( {2\; A} \right)}\begin{Bmatrix}{{4\; I_{dc}{\cos \left( {2\; P} \right)}} - {A_{2}\left\lbrack {3 + {\cos \left( {4\; P} \right)}} \right\rbrack} -} \\{B_{2}{\sin \left( {4\; P} \right)}}\end{Bmatrix}}\end{matrix}}{2\; {\sin^{2}\left( {2\; A} \right)}}} & (19) \\{N = \frac{\begin{matrix}{{4\; I_{dc}{\cos \left( {2\; P} \right)}} - {A_{2}\left\lbrack {3 + {\cos \left( {4\; P} \right)}} \right\rbrack} +} \\{{2\; {{\cos \left( {2\; A} \right)}\left\lbrack {{2\; I_{dc}} - {A_{2}{\cos \left( {2\; P} \right)}} - {B_{2}{\sin \left( {2\; P} \right)}}} \right\rbrack}} -} \\{B_{2}{\sin \left( {4\; P} \right)}}\end{matrix}}{\begin{matrix}{{4\; I_{dc}} - {2\; A_{2}{\cos \left( {2\; P} \right)}} - {2\; B_{2}{\sin \left( {2\; P} \right)}} +} \\{{\cos \left( {2\; A} \right)}\begin{Bmatrix}{{4\; I_{dc}{\cos \left( {2\; P} \right)}} - {A_{2}\left\lbrack {3 + {\cos \left( {4\; P} \right)}} \right\rbrack} -} \\{B_{2}{\sin \left( {4\; P} \right)}}\end{Bmatrix}}\end{matrix}}} & (20) \\{C = \frac{{\sin \left( {2\; A} \right)}\begin{Bmatrix}{{A_{2}{\sin \left( {4\; P} \right)}} + {B_{2}\left\lbrack {3 - {\cos \left( {4\; P} \right)}} \right\rbrack} -} \\{4\; I_{dc}{\sin \left( {2\; P} \right)}}\end{Bmatrix}}{\begin{matrix}{{4\; I_{dc}} - {2\; A_{2}{\cos \left( {2\; P} \right)}} - {2\; B_{2}{\sin \left( {2\; P} \right)}} +} \\{{\cos \left( {2\; A} \right)}\begin{Bmatrix}{{4\; I_{dc}{\cos \left( {2\; P} \right)}} - {A_{2}\left\lbrack {3 + {\cos \left( {4\; P} \right)}} \right\rbrack} -} \\{B_{2}{\sin \left( {4\; P} \right)}}\end{Bmatrix}}\end{matrix}}} & (21)\end{matrix}$

The solutions for the unknown parameters are obtained by Equations (19)to (21) Therefore, when the experimental values for I_(dc), A₂, and B₂are obtained using the Equations (10) to (12), the obtained experimentalvalues are substituted into the Equations (19) to (21) to obtain theexperimental values for the unknown parameters. When the experimentalvalue of the I₀₀ measured for one sample is divided by the experimentalvalue of T_(s) measured by removing the sample and forming the opticalsystem in a straight state, the experimental value R_(u) of thenon-polarization reflectivity due to the sample can be obtained.Therefore, the experimental values of R_(u), N, and C that areparameters related to the properties of the sample are measured and thetheoretical Equation therefor can be established and therefore, thevalues of the theoretical Equation established using the least-squaresalgorithm coincide with the experimental values, thereby obtaining theproperties of the sample. The method may be applied to severalcombinations of selecting at least three of five simultaneous Equations(14) to (18) to obtain the experimental values of R_(u), N, and C. Inthis case, when the number of simultaneous Equations is 4 or 5, thenumber of simultaneous Equations is reduced by the number of unknownparameters by operations such as addition, subtraction, or division of apart of the simultaneous Equations, and the like, thereby obtaining thesolution for the unknown parameters. For example, when the simultaneousEquations (15) to (18) are selected, the following Equations (22) to(24) are given.

$\begin{matrix}{I_{00} = \frac{\begin{matrix}{{2\left\lbrack {{U_{2}{\cos \left( {2\; P} \right)}} + {V_{2}{\sin \left( {2\; P} \right)}} - {2\; U_{4}}} \right\rbrack} +} \\{{\cos \left( {2\; A} \right)}\left\lbrack {U_{2} - {4\; U_{4}{\cos \left( {2\; P} \right)}} - {V_{2}\cos \left( {4\; P} \right)} - {U_{2}{\sin \left( {4\; P} \right)}}} \right\rbrack}\end{matrix}}{2\; {{\sin^{2}\left( {2\; A} \right)}\left\lbrack {{\cos \left( {4\; P} \right)} + {\sin \left( {4\; P} \right)}} \right\rbrack}}} & (22) \\{N = \frac{\begin{matrix}{U_{2} - {4\; U_{4}{\cos \left( {2\; P} \right)}} - {V_{2}\cos \left( {4\; P} \right)} +} \\{2\; {{\cos \left( {2\; A} \right)}\left\lbrack {{U_{2}{\cos \left( {2\; P} \right)}} - {2\; U_{4}} + {V_{2}{\sin \left( {2\; P} \right)}}} \right\rbrack}} \\{{- U_{2}}{\sin \left( {4\; P} \right)}}\end{matrix}}{\begin{matrix}{{2\; U_{2}{\cos \left( {2\; P} \right)}} - {4\; U_{4}} + {2\; V_{2}{\sin \left( {2\; P} \right)}} +} \\{{\cos \left( {2\; A} \right)}\left\lbrack {U_{2} - {4\; U_{4}{\cos \left( {2\; P} \right)}} - {V_{2}{\cos \left( {4\; P} \right)}} - {U_{2}{\sin \left( {4\; P} \right)}}} \right\rbrack}\end{matrix}}} & (23)\end{matrix}$

Here, U₂=A₂+B₂, U₄=A₄+B₄, and V₂=A₂−B₂.

In Equations (14) to (18), the Fourier coefficients such as I_(dc)/I₀₀,A₂/I₀₀, B₂/I₀₀, A₄/I₀₀, and B₄/I₀₀ or I_(dc)/T₀₀, A₂/I_(dc) B₂/I_(dc),A₄/I_(dc), and B₄/I_(dc) are the properties of the sample and thefunctions of the azimuths of the first polarizer and the third polarizerand therefore, the properties of the sample may be immediately obtainedfrom the experimental values thereof.

The normalized Fourier coefficients from the non-normalized Fouriercoefficients of Equations (15) to (18) are obtained by the followingEquations (25) to (28).

α₂ =A ₂ /I _(dc)  (25)

β₂ =B ₂ /I _(dc)  (26)

α₄ =A ₄ /I _(dc)  (27)

β₄ =B ₄ /I _(dc)  (28)

When only the α₂ and β₂ among the normalized Fourier coefficients areselected, they are obtained by the following Equations (29) and (30).

$\begin{matrix}{C = \frac{{\sin \left( {2\; A} \right)}\left\lbrack {{U_{2}{\cos \left( {4\; P} \right)}} + {4\; U_{4}{\sin \left( {2\; P} \right)}} - {V_{2}{\sin \left( {4\; P} \right)}} - V_{2}} \right\rbrack}{\begin{matrix}{{2\; U_{2}{\cos \left( {2\; P} \right)}} - {4\; U_{4}} + {2\; V_{2}{\sin \left( {2\; P} \right)}} +} \\{{{\cos \left( {2\; A} \right)}\left\lbrack {U_{2} - {4\; U_{4}{\cos \left( {2\; P} \right)}} - {V_{2}{\cos \left( {4\; P} \right)}}} \right\rbrack} -} \\{U_{2}{\sin \left( {4\; P} \right)}}\end{matrix}}} & (24)\end{matrix}$

When the simultaneous equations (15) to (18) are selected, in theequations (23) and (24), the values of N and C can each be obtained bysubstituting U₂=α₂+β₂, U₄=α₄+β₄, and V₂=α₂−β₂. Therefore, when a part ofthe Fourier coefficients having the relatively excellent measurementcondition is selected, the values of N and C may be obtained therefrom.The ellipsometric angles are calculated by the following Equations (31)and (32).

$\begin{matrix}{\Psi = {\frac{1}{2}{\cos^{- 1}(N)}}} & (31) \\{\Delta = {\cos^{- 1}\left( \frac{C}{\sqrt{1 - N^{2}}} \right)}} & (32)\end{matrix}$

The relationship Equation between the Fourier coefficients and theellipsometric angles in the case of the rotating-element multichannelspectroscopic ellipsometers of the present invention as shown in FIG. 3is obtained by replacing the azimuth P with A and the azimuth A with Pin the above Equations (14) to (30) of FIG. 2.

In the case of the semiconductor industry, a size of the test region tobe measured in the sample is very small at several tens of μm andtherefore, as in FIGS. 2 and 3, the achromatic aberration optical focussystem 450 that focuses the incident light 100 on a test region in thesample 200 is installed in a path in front of the sample stage 210 andthe achromatic aberration collimator 460 that again changes the lightreflected or transmitted by the sample 200 into the parallel light maybe selectively provided. Here, the achromatic aberration optical focussystems 330 and 450 and the achromatic aberration collimators 120 and460 may be configured of an optical system including at least one mirrorfor correcting chromatic aberration for the broadband wavelength or atleast one lens made of heterogeneous materials, or at least one mirrorand at least one lens and may adopt the lenses or the mirrors coatedwith a single thin film or a multi-layer thin film in order to improvetransmission efficiency or reflection efficiency.

The sample stage 210 may be configured a 6 free degree system that canimplement a parallel movement of 3 free degrees vertically andhorizontally and includes a gradient control having 2 free degrees and arotation function in order to change the alignment and the measuredposition of the sample 200 and may include a vacuum chuck in order tomaintain the sample on the sample stage in a stop state at the time ofmeasurement.

For the alignment of the sample for measurement, a sample alignmentsystem including a laser emitting light for sample alignment, an opticalsystem inputting light emitted from the laser to the sample in aspecific direction, and a photometric detector receiving light reflecteddue to the sample with respect to the incident light and determining theposition of the received light may be provided.

In order to reduce the error due to the change in the measuringenvironment, the multichannel spectroscopic ellipsometer of the presentinvention may include an apparatus that makes the optical path into theatmospheric state of nitrogen gas or argon gas, and the like, to measurethe broadband wavelength and in order to reduce an effect due to thevibration of the system and the measuring environment, the multichannelspectroscopic ellipsometer may be mounted on a vibration isolationsystem and may include a constant temperature system in order to reducethe measuring error due to the change in temperature for the lightsource, the optical elements, the sample, and the multichannelspectrometer.

In particular, in the case of the semiconductor industries, it isimportant for the multichannel spectroscopic ellipsometer to measure theplurality of wafer samples in a rapid time. To this end, themultichannel spectroscopic ellipsometer may include a sample containercapable of storing samples and a sample delivery apparatus thatsequentially takes out the samples from the sample container and movesthe samples to the sample stage and when the measurement for thedesignated points completes, again delivers the sample disposed on thesample stage on the sample container so as to measure the properties ofthe sample.

The multichannel spectroscopic ellipsometer according to the exemplaryembodiment of the present invention may analyze various properties suchas interfacial characteristic, a thin film thickness, a complexrefractive index, a nano shape, anisotropic characteristic, surfaceroughness, a composition ratio, crystallinity, and the like, of thesample from the measured Fourier coefficients or the measuredellipsometric functions.

The multichannel spectroscopic ellipsometer can be used for measuringequipment for a semiconductor device process, measuring equipment for aflat display process, measuring equipment for a solar cell, measuringequipment for a thin film optics, a bio sensor, or a gas sensor, and thelike.

In particular, in the multichannel spectroscopic ellipsometer accordingto the exemplary embodiment of the present invention, a method foranalyzing properties in the case in which an analysis method such as amethod for measuring a nano pattern shape is very complex first obtainsthe measuring data of the Fourier coefficients or the ellipsometricfunctions for the sample, establishes the optical theory for the sample,obtains the data of the Fourier coefficients or the ellipsometricfunctions calculated using the values of the plurality of unknownparameters defined in the region set for the established theoreticalequation, forms the continuous function for the unknown parameters forthe calculated data, and optimizes the continuous function by applyingthe least-squares algorithm to the measuring data, thereby obtaining theproperties of the sample. In this case, the multichannel spectroscopicellipsometer according to the exemplary embodiment of the presentinvention may include a large-capacity high-speed operation systemconfigured of a high-performance parallel computer, a rigorouscoupled-wave analysis (RCWA) algorithm based analysis software, and alarge-capacity data storage so as to rapidly find the properties of thesample from the measuring data of the Fourier coefficients or theellipsometric functions measured for the sample.

The multichannel spectroscopic ellipsometer according to the exemplaryembodiment of the present invention may include an apparatus thatrotates in a single direction or plurality of measuring directions tothe sample, or in the single or plurality of azimuths P and A, or in thesingle or plurality of incident angles θ to measure the sample.

The multichannel spectroscopic ellipsometer according to the exemplaryembodiment of the present invention can measure the Mueller matrixcomponents of the sample to analyze the properties of the sample.

In the multichannel spectroscopic ellipsometer according to theexemplary embodiment of the present invention, in order to obtain themeasured values for the entire region of 0° to 360° for Δ representingthe phase difference among the ellipsometric functions, at least onecompensator disposed before or after the sample stage 210 on theprogress path of light of FIGS. 2 and 3 may be provided.

By the configuration as described above, the rotating-elementellipsometer according to the exemplary embodiment of the presentinvention can more easily measure the Fourier coefficients for awaveform of the intensity of light by controlling the integration timeand the measuring frequency of exposure according to the intensity oflight by solving the problems of the limitation of the integration timeof the photometric detector in the rotating-element ellipsometer of therelated art.

The rotating-element ellipsometer according to the exemplary embodimentof the present invention can improve the measuring precision by rapidlyand easily changing the integration time and the measuring frequency ofexposure with the computer software.

According to the exemplary embodiment of the present invention, theFourier coefficients for the waveform of the intensity of light are moreeasily acquired by improving the measuring precision without adding theoptical system and the Fourier coefficients for the waveform of theintensity of light are more precisely acquired by the simplecalculation, thereby accurately measuring the properties of the sample.

By the foregoing means, the rotating-element multichannel spectroscopicellipsometer according to the exemplary embodiment of the presentinvention is configured of three linear polarizers having the anachromatic aberration characteristics to optimally perform thespectroscopic measurement of the broadband wavelength region and solvesthe residual polarization problem of the light source and thepolarization dependency problem of the multichannel photometric detectorto improve the measuring accuracy.

The multichannel spectroscopic ellipsometer according to the exemplaryembodiment of the present invention includes the digital signalmodulating apparatus to easily change the measuring period, themeasuring frequency of exposure, and the integration time so as toimplement better measuring conditions, thereby more rapidly andaccurately measuring the properties of the sample in real time.

The present invention is not limited to the aforementioned exemplaryembodiment and an application range is various and it is apparent thatvarious modifications can be made to those skilled in the art withoutdeparting from the spirit of the present invention described in theappended claims.

1. An ellipsometer including a light source, a polarization modulatingunit, a sample stage, a polarization analysis unit, and a photometricdetector, the ellipsometer comprising: a digital signal modulatingapparatus connected to an optical element unit rotating at constantvelocity of the polarization modulating unit or the polarizationanalysis unit to control a measuring frequency of exposure of thephotometric detector, the integration time and the measuring frequencyof exposure of the photometric detector are controlled according to theintensity of light irradiated to the photometric detector.
 2. Theellipsometer of claim 1, further comprising: an operator acquiring aplurality of values of exposure for a waveform of the intensity of lightat a predetermined interval for any multiple of the period from thephotometric detector and performing discrete Fourier transform on theplurality of values of exposure to determine a plurality of Fouriercoefficients and average value component for the waveform of theintensity of light, wherein the intensity of light may be changed at apredetermined period over time.
 3. The ellipsometer of claim 2, whereinthe value of exposure S_(j) is measured by S_(j)=∫_((j-1)pT/M+T) _(d)^((j-1)pT/M+T) ^(d) ^(+T) ^(i) I(t)dt, (j=1, 2, 3, . . . , M) andnon-normalized Fourier coefficients A_(2n) and B_(2n) of waveform ofintensity of light and average value I_(dc) of intensity of light eachare obtained by$A_{2\; n} = {\frac{\xi_{2\; n}}{T_{i}{\sin \left( \xi_{2\; n} \right)}}\left\{ {{a_{2\; n}{\cos \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}} - {b_{2\; n}{\sin \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}}} \right\}}$$B_{2\; n} = {\frac{\xi_{2\; n}}{T_{i}{\sin \left( \xi_{2\; n} \right)}}\left\{ {{a_{2\; n}{\sin \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}} + {b_{2\; n}{\cos \left\lbrack {\xi_{2\; n}\left( {1 + \frac{2\; T_{d}}{T_{i}}} \right)} \right\rbrack}}} \right\}}$I_(dc) = d₀/T_(i) where {T: Dynamic turn period of optical elementrotating at constant velocity P: The number of measuring periods(positive multiple of ½) M: Measuring frequency of exposure atpredetermined time interval for measuring period pT T_(d): Delay timeT_(i): Integration time${I(t)} = {I_{dc} + {\sum\limits_{n = 1}^{N}\; \left\lbrack {{A_{2\; n}{\cos \left( {4\; \pi \; {{nt}/T}} \right)}} + {B_{2\; n}{\sin \left( {4\; \pi \; {{nt}/T}} \right)}}} \right\rbrack}}$I(t): Intensity of light I_(dc): Average value of intensity of light or0-order Fourier coefficient A_(2n), B_(2n): Fourier coefficients 2N:Natural number representing highest order among Fourier coefficientsexcept for 0$\left. {{\xi_{n} = \frac{n\; \pi \; T_{i}}{T}}{a_{2\; n} = {\frac{2}{M}{\sum\limits_{j = 1}^{M}\; {S_{j}{\cos \left( \frac{4\; n\; {\pi \left( {j - 1} \right)}p}{M} \right)}}}}}{b_{2\; n} = {\frac{2}{M}{\sum\limits_{j = 1}^{M}\; {S_{j}{\sin \left( \frac{4\; n\; {\pi \left( {j - 1} \right)}p}{M} \right)}}}}}{d_{0} \equiv {\frac{1}{M}{\sum\limits_{j = 1}^{M}\; S_{j}}}}} \right\}$4. The ellipsometer of claim 3, wherein properties for the sample ofinterfacial characteristic, a thin film thickness, a complex refractiveindex, a nano shape, anisotropic characteristic, surface roughness, acomposition ratio, crystallinity are analyzed from the Fouriercoefficients (I_(dc)/I₀₀, A_(2n)/I₀₀, B_(2n)/I₀₀; n=1, 2, 3, . . . ) or(I_(dc)/I₀₀, A_(2n)/I_(dc), B_(2n)/I_(dc); n=1, 2, 3, . . . )
 5. Theellipsometer of claim 3, wherein ellipsometric functions are obtained bylimitedly selecting a part of the Fourier coefficients I_(dc), A_(2n),B_(2n); n=1, 2, 3, . . . ).
 6. The ellipsometer of claim 1, wherein theellipsometer is any one of rotating-element ellipsometers. 7-20.(canceled)